1. Field of the Invention
The present invention relates to an in-plane switching mode liquid crystal display (LCD) and its fabrication method. More particularly, the present invention relates to an in-plane switching (IPS) mode LCD and its fabrication method capable of improving picture quality by enhancing a luminance characteristic and also capable of reducing resistance of common lines.
2. Discussion of the Related Art
As consumer interest in information displays is growing and the demand for portable (mobile) information devices is increasing, research and commercialization of light and thin flat panel displays (“FPD”) has also increased. Among FPDs, the liquid crystal display (“LCD”) is a device for displaying images by using optical anisotropy of liquid crystal. LCD devices exhibit excellent resolution and color and picture quality. So, the LCD device may be widely applied for notebook computers or desktop monitors, and the like.
The LCD includes a color filter substrate, an array substrate and a liquid crystal layer formed between the color filter substrate and the array substrate.
The color filter substrate includes a color filter having a plurality of sub-color filters that implement red, green and blue colors, a black matrix for dividing the sub-color filters and blocking light transmission through the liquid crystal layer, and a transparent common electrode for applying voltage to the liquid crystal layer.
The array substrate includes gate lines and data lines which are arranged vertically and horizontally to define a plurality of pixel regions, TFTs, switching elements, formed at respective crossings of the gate lines and the data lines, and pixel electrodes formed on the pixel regions.
The color filter substrate and the array substrate are attached in a facing manner by a sealant (not shown) formed at an edge of an image display region to form a liquid crystal panel. The attachment of the color filter substrates and the array substrate is made by an attachment key formed on the color filter substrate or the array substrate.
The above described LCD is an example of a twisted nematic (TN) type LCD in which nematic liquid crystal molecules are driven in a direction perpendicular to the substrates. The TN type LCD has shortcomings in that its viewing angle is quite narrow. This results from refractive anisotropy of liquid crystal molecules such that when a voltage is applied to a liquid crystal display panel, liquid crystal molecules which have been aligned horizontally to the substrates are aligned substantially in the vertical direction to the substrates.
Thus, an in-plane switching (IPS) mode LCD, in which liquid crystal molecules are driven in a horizontal direction to the substrates has been introduced to improve the viewing angle.
FIG. 1 is a plan view showing a portion of an array substrate of the related art IPS mode LCD. The N number of gate lines and the M number of data lines are formed to cross each other to define the M×N number of pixels on an array substrate. One pixel is shown on the drawing merely for the sake of brevity.
FIG. 2 is an exemplary view showing a cross-section take along line I-I′ of the array substrate in FIG. 1, in which the array substrate and the color filter substrate attached to the array substrate are shown together.
As shown in FIGS. 1 and 2, a gate line 16 and a data line 17 are formed vertically and horizontally to define a pixel region on the transparent array substrate 10, and a TFT (T), a switching element, is formed at the crossing of the gate line 16 and the data line 17.
The TFT (T) includes a gate electrode 21 connected with a gate line 16, a source electrode 22 connected to the data line 17 and a drain electrode 23 connected to a pixel electrode 18 via a pixel electrode line 18l. The TFT also includes a first insulation film 15a for insulating the gate electrode 21, source and drain electrodes 22 and 23, and an active pattern 24 for forming a conductive channel between the source electrode 22 and the drain electrode 23 by a gate voltage supplied to the gate electrode 21.
Reference numeral 25 denotes an ohmic contact layer for ohmic-contacting between source and drain regions of the active pattern 24 and the source and drain electrodes 22 and 23.
In the pixel region, a common line 8l and a storage electrode 18s are arranged in a direction parallel to the gate line 16, and a plurality of common electrodes 8 and a plurality of pixel electrodes 18 are arranged to be parallel to the data line 17 and generate an in-plane field 90 to switch the liquid crystal molecules 30.
The plurality of common electrodes 8 are simultaneously formed with the gate line 16 and connected to the common line 8l, and the plurality of pixel electrodes 18 are simultaneously formed with the data line 17 and connected to the pixel electrode line 18l and the storage electrode 18s. 
The pixel electrodes 18 connected to the pixel electrode line 18l are electrically connected to the drain electrode 23 of the TFT (T) via the pixel electrode line 18l. 
The storage electrode 18s overlaps a portion of the lower common line 8l with the first insulation film 15a interposed therebetween to form a storage capacitor Cst.
On a transparent color filter substrate 5, there are formed a black matrix 6 for preventing a leakage of light to the TFT (T), the gate line 16 and the data line 17, and a color filter 7 for implementing red, green and blue colors.
An alignment film (not shown) for determining an initial alignment direction of the liquid crystal molecules 30 is coated on facing surfaces of the array substrate 10 and the color filter substrate 5.
In the related art in-plane mode LCD having the above-described structure, the common electrodes 8 and the pixel electrodes 18 are formed on the same array substrate 10 to generate the in-plane field. As such, the viewing angle can be improved.
However, because the common electrodes 8 and the pixel electrodes 18 made of an opaque material are disposed in the pixel region for image display, an aperture ratio is degraded which degrades luminance.
In addition, the in-plane field is not normally formed within the pixel region due to a signal interference between the data line 17 and the pixel electrode 18. So, in order to prevent this, the line width of the common electrode 8 adjacent to the data line 17 is increased, which, however, further degrades the aperture ratio.